Maintaining a specified climate is just as important a function of a building as the structural and shelter functions. Energy consumption for climate control is frequently the major operating expense of buildings. Various materials and systems have previously been employed to conserve heat or cool in buildings thereby reducing the energy cost. Such previous materials in systems have included large basement tanks of water, walls made from drums of water, ponds of water on tops of roofs, thick cement walls, boxes of rocks, fibre glass or other fibrous sheets of insulation, and dead air spaces as in insulating glass or other insulating panels. Previous systems have also employed phase change materials in liquid or other non-rigid suspension mediums lacking structural characteristics or otherwise failing to serve any architectural purpose in addition to its heat storage function.
Others have recognized that if the duty cycle of existing fuel fired heating, ventilation and air conditioning systems (HVAC) could be extended without offsetting costs, significant savings could be achieved. In a recent study funded by the Energy Research and Development Agency (ERDA) it was concluded that the short firing time (duty cycle) of the typical space heater in buildings is the largest single contributor to inefficiency and fuel wastage in space heating.
Others have proposed use of modular storage units using PCM to improve the duty cycle of space heaters and air conditioners, but previously it has not been possible to attain a commercially acceptable cycle life for the PCM. See Telkes, Maria, Heating and Ventilating, November 1949; Refrigeration Engineering, July 1952, Page 712; Hodgins, TW and Hoffman TW, Canadian Journal of Technology, Volume 33, Page 293; and Edison Electric Institute Bulletin, 27 (6): 250.